1. Field of the Invention
The instant invention relates to wire line core retrieval systems for diamond drilling exploration.
2. Description of the Related Art
Core barrels are used frequently in mineral exploration, where the coring may be several hundred to several thousand feet in length. Exploration diamond core drilling utilizes an annular diamond-impregnated drill bit attached to the end of hollow drill rods to cut a cylindrical core of solid rock. The core samples are recovered and examined for mineral percentages and stratigraphic contact points.
Core barrels comprise generally three main components, including a barrel head, outer steel tube to which the core bit is attached and an inner tube which is attached to the barrel head via a set of bearings. The outer tube or outer barrel rotates with the core bit attached to it and cuts the core, whereas the inner barrel on its bearings does not rotate so that the core entering the inner barrel is not disturbed. At the bit end of the inner barrel is a core retainer box and spring, which holds the core inside the barrel while the barrel is pulled out of the hole. If the core is still attached to the bottom of the bore hole it will grip the core firm enough for the barrel to be pulled back and snap the core from the bottom of the hole. Once the core barrel is full, the drill rods and barrel are pulled out of the hole and the core is removed.
Wire-line coring is the act or process of core drilling with a wire-line core barrel. In wireline drilling the barrels work the same way except the drill rods used with this barrel are thin wall tubes of the same outside and inside diameters as the outer tube of the barrel, and the inner barrel with its barrel head containing the bearing are lowered down inside the drill rods by means of a device called an overshot. When the barrel is full of core the overshot is lowered down inside the rods and latches onto the inner barrel at the same time the inner barrel locking latches are released and the inner barrel with its core are pulled out by the winch line. As a result, wireline core drilling is a faster process of recovering the core, eliminating the time consuming process of retrieving the core barrel every time it is full of core.
Since the drill strings in wireline coring are made up of various tubes, only the outer of which is rotating, certain coupling mechanisms must be employed. To removably retain the core barrel inner tube assembly adjacent to the core bit a locking coupling must be utilized. In the prior art, the outer tube assembly is composed of an adaptor coupling that is threadedly connected to the core barrel outer tube to provide a recess in which a landing ring (drill string landing shoulder) is mounted, a remaining shell connected to the inner (lower) end of tube and an annular drill bit at the inner end of the reaming shell for drilling into the earth formation from which the core sample is taken. The outer end of the assembly includes a locking coupling that connects the adaptor coupling to the adjacent pipe section of the drill string. At the opposite end of the coupling from the pipe section, the locking coupling, in conjunction with the annular recess of the coupling, forms a latch seat inside of the surface of the adaptor coupling against which the latches are seatable for removably retaining the core barrel inner tube assembly adjacent to the core bit. In the prior art, the latch assemblies comprise pivotal, spring-loaded arms which are in axial relationship to the core barrel inner tube.